Medical device, apparatus, and surgical method

ABSTRACT

A medical that is implantable into a human or animal body or being an augmentation device for strengthening human or animal hard tissue for subsequent implantation of a separate implant. The device includes a sheath element suitable of being brought into contact, during a surgical operation, with live hard tissue and/or with hard tissue replacement material. The sheath element has a, for example, generally elongate shape and a longitudinal bore defining a longitudinal opening reaching from a proximal end of the sheath element into a distal direction, and a plurality of holes in a wall of the opening. Further, the device includes a liquefiable element that is insertable or inserted in the longitudinal opening and at least partly liquefiable by the impact of energy impinging from the proximal side.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is in the field of medical technology. In particular, itrelates to medical devices, medical apparatus and medical methods,especially to implants, apparatuses for implantation, and implantationmethods.

Description of Related Art

If screws are anchored in live bone tissue, often the problem ofinsufficient bone stability or insufficient stability of the anchoringin the bone arises. Especially, in trabecular bone tissue, any loadacting on the screw is passed over to only few trabeculae, with adverseconsequences both for the load bearing capability of the screw-boneconnection and for its long-time stability. This is especially severe inosteoporotic or osteopenic or otherwise weakened bone tissue.

One solution of this problem is the use of an alternative anchoringmethod that is suitable also for tissue in which screws are not stable.The publications WO 02/069817, WO 2004/017 857, WO 2008/034 277, and WO2009/055 952 concern anchorage of an implant in bone tissue with the aidof mechanical vibration and a thermoplastic material which isliquefiable by the mechanical vibration, i.e. the thermoplastic materialis capable of being liquefied when vibrated and simultaneously kept incontact with a non-vibrating surface. The thermoplastic material, wherein contact with the bone tissue, is liquefied and pressed into pores orcavities of the bone tissue to constitute, when re-solidified, apositive fit connection with the bone tissue.

A special group of embodiments of implants and implant anchoringprocesses is based on the liquefiable material being inserted(pre-assembled or inserted in situ) in a longitudinal bore of a sheathelement. The sheath element comprises at least one hole in the sheathelement wall, through which the liquefied material is pressed from thelongitudinal bore into the structures (pores or cavities or otherstructures) of the bone tissue or other hard tissue or hard tissuereplacement material in which anchoring is desired. This principle ofpressing liquefied material out of a tube or sleeve element with lateralopenings is for example described in U.S. Pat. Nos. 7,335,205,6,921,264, WO 2009/055 952, WO 2009/010247, WO 2009/010234, and PCTapplication No. PCT/CH 2009/000138, all of which are incorporated hereinby reference.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a medical devicebeing an implant or an augmentation device overcoming drawbacks of priorart implants or augmentation devices. It is a further object of theinvention to provide an improved implant that comprises a sheath elementand a plurality of holes through which liquefied liquefiable material ispressed into adjacent hard tissue and/or hard tissue replacementmaterial.

In accordance with an aspect of the invention, a medical device isprovided, the device, for example, being implantable into a human oranimal body or being an augmentation device for strengthening human oranimal hard tissue for subsequent implantation of a separate implant,the device comprising a sheath element suitable of being brought intocontact, during a surgical operation, with live hard tissue and/or withhard tissue replacement material. The sheath element has a for examplegenerally elongate shape and a longitudinal bore defining a longitudinalopening reaching from a proximal end of the sheath element into a distaldirection, and a plurality of holes in a wall of the opening. At leasttwo of the holes may have an approximately equal axial position.Further, the device comprises a liquefiable element that is insertableor inserted in the longitudinal opening and at least partly liquefiableby the impact of energy impinging from the proximal side so thatliquefied material flows through the holes in the wall and out of thelongitudinal opening into structures of the hard tissue and/or hardtissue replacement material. The medical device also comprises adirecting structure that is structured angularly with respect to alongitudinal axis of the longitudinal opening to direct differentportions of the liquefiable material to different ones of the holes.

‘Structured angularly’—or azimuthally—means that the structure is notconstant along the circumference but varies as a function of theazimuthal angle. In this, the directing structure is a structure withinthe cross section of the longitudinal bore, i.e. if, for example, thelongitudinal bore has a circular cross section, the directingstructure's radial position is at least partly within the radius of thebore.

The holes in the wall of the sheath element (often in thecircumferential wall) may be approximately equally distributed aroundthe periphery, or they may be asymmetrically distributed. For example,for certain applications it may be advantageous to have two or threeholes at relatively small angular distances of between 30° and 120°,whereas on the other side of the sheath element no holes are present.

The longitudinal bore may be centric or arranged off-center. While formany applications a centric arrangement may be advantageous, forasymmetric implants (such as the shaft of a prosthesis) of for implantsfrom which the outflow is to be asymmetric may be better. Especially,the positioning of the longitudinal bore with respect may influence thedead volume of thermoplastic material remaining in the hole—the thinnerthe wall at the position of the hole, the less deep the hole, and thesmaller the dead volume.

The liquefiable element may be a single, one-piece element. Such asingle one-piece element may be advantageous in terms of transmittingmechanical energy from a proximal to a distal end. Alternatively, aplurality of liquefiable elements may be present, such as a plurality ofshaped pieces, chips, flakes, etc.

In a medical device according to this principle, the liquefaction takesplace by the impinging energy being absorbed in a vicinity of the distalend of the liquefiable element and in a vicinity of the holes. Forexample, the impinging energy may be mechanical vibration energy, andmaterial of the liquefiable element may be liquefied at an interfacebetween the liquefiable element and the directing structure.

The directing structure is then formed by a stop face, against which thedistal end of the liquefiable element is pressed during liquefaction.The distal stop face for the liquefiable element may, for example, closeoff the longitudinal opening towards the distal side or at leastsubstantially reduce (by for example at least 50%) a distal portion ofthe longitudinal opening's cross section compared to the proximalportion. An optional, remaining cross section of the longitudinalopening distal portion extending distally from the directing structuremay for example serve as a, for example, central (off-centerconfigurations are possible) guiding portion or as a distal hole throughwhich liquefied material portions, depending on the depth and on thediameter of such a distal hole, may be pressed out in addition to theholes in wall of the sheath element.

The directing structure angularly structures the volume proximally ofthe distal end of the liquefiable element so that different portions ofthe liquefied material are directed to a determined one of the holes.

It has been found that by this approach, a potential problem encounteredwith prior art medical devices is solved. If the tissue adjacent todifferent holes was significantly different in terms of porosity and/orhardness, it could happen that a large part of the liquefied materialexited through the one hole where the least resistance for thehydrostatic pressure on the liquefied material is encountered. Thiscould result in an anchoring that is undesirably anisotropic. Due to theapproach according to the first aspect of the invention, there is a morehomogeneous distribution of liquefiable material between the holes.

In embodiments of the invention, the directing structure comprises atleast one wall protruding proximally from the directing structure body.The wall separates sub-volumes of a distal region of the longitudinalopening where the liquefaction takes place. In this, the wall does notneed to have a homogeneous thickness but merely makes an angularseparation between different volume sections of the longitudinal openingthat each communicate with the different holes, so that portions of theliquefiable material in these volume portions will have a strongtendency or even be forced to exit the longitudinal portions through theparticular attributed hole.

In addition to making this angular separation, the wall also serves asenergy director where vibration energy tends to be absorbed and wherethere liquefaction sets in. Due to this, the liquefaction may set inabove the holes ('above' here is used to refer to the proximaldirection; this does not imply a particular orientation during use) orat least above their distal end, so that a blocking of the holes byremaining solid parts may be reduced or prevented.

In an embodiment, the directing structure further comprises a rampportion that slopes away from the longitudinal axis towards a distal endof the according hole, so that there is no pronounced edge between thewall and the stop face. The ramp portion may be curved. It may comprisea radius geometry that guides the liquefiable material from an axial toa radial direction within the sheath element.

The wall may protrude further to the proximal direction than holes' mostproximal side so that every material that reaches the hole is confinedto the volume segment by the wall and is, thus, prevented from gettingto an other wall by the hydrostatic pressure acting on the liquefiablematerial and by its movement. These embodiments are especially suitedfor cases where a large difference between the resistances encounteredfor material flowing out of the different holes is to be expected. Inother embodiments, the wall protrudes less far the to proximal side thanthe holes' most proximal portion, but nevertheless the directing effectis there. Preferably, the wall protrudes to at least ¼, at least ⅓ or toat least ½ of the axial extension of the hole or of at least one holethat is adjacent (measured from the most distal side of the holes).

In a first group of embodiments, the directing structure is a structureof the sheath element, i.e. its body is one-piece with the sheathelement or rigidly and ex-situ fastened to it.

In a second group of embodiments, the directing structure is a directingstructure of an insert element that is insertable in situ. The sheathelement's longitudinal bore may then be a through bore reaching from theproximal to the distal end. The sheath element further comprises a stopstructure cooperating with the insert element when the latter isinserted from the proximal side to stop the insert element at a desiredaxial position and to secure it there against more distal movements. Thestop structure in general is achieved by the longitudinal borecomprising a non-homogeneous cross section along its longitudinaldirection. It may, for example, comprise a shoulder that cooperates witha tapering distal portion of the insert element to form a force fit.

In embodiments of the second group, the longitudinal bore is used as acannulation that may be used in minimally invasive surgery for guidingthe device during insertion.

The device according to the first aspect may be an implant, such as animplant used for anchoring. The implant may be a bone screw and inaddition to the anchoring by the liquefiable material comprise a thread.It may alternatively be an implant replacing a bone screw. More ingeneral, the invention relates to any implant that is destined to beanchored in hard tissue and/or hard tissue replacement material.

As an alternative to being an implant, the device according to the firstaspect of the invention may be an augmentation device used foraugmenting, for example, weak or brittle hard tissue and/or hard tissuereplacement material and for thereafter being removed.

Depending on whether the device is an implant or an augmentation device,the walls and/or the holes may be chosen to have appropriate dimensions.Holes with comparably large cross sections are suited for ensuring astrong connection between liquefied and re-solidified material that hasflown out of the holes and into structures of the hard tissue and/orhard tissue replacement material. This is useful if the device is toremain implanted, i.e. if it is an implant. Holes with comparablysmaller cross sections may be used for augmentation devices—the smallercross sections at least referring to the circumferential dimension; theaxial extension may also then be optionally greater; for example, theholes may be elongate slits over more than one thread turns.

Further, the holes may optionally be chosen to be not strictly radial,so that the holes are asymmetric with respect to clockwise vs.anticlockwise rotation of the sleeve element around its longitudinalaxis. If the sleeve element having this optional feature also has athread, this feature may on the one hand be used in an implant toenhance the resistance against an unscrewing twist when the force actingon the liquefied and re-solidified material is not a pure shear force,but has a radial component. It may on the other hand be used in anaugmentation device to be removed by favouring separation betweenliquefiable material within the sheath element and liquefiable materialthat has flown out of it.

In embodiments, the device may be a pedicle anchor device. The pedicleanchor device is equipped for being used like a pedicle screw, i.e. forbeing implanted in the vertebra from a dorsal direction (but generallyat an angle to the sagittal plane, slightly inward towards the sagittalplane) through the pedicle so that a distal portion of the deviceprotrudes into the vertebral body. A proximal portion of the pedicleanchor device has a head portion that serves for securing an orthopaedicrod or other device that stabilizes the spinal column. The pedicleanchor device, thus, has a head portion and a shaft portion. The shaftportion is capable of being anchored, like a pedicle screw shaft(sometimes referred to as ‘stem’), in the vertebra. The head portionmay, for example, be formed like head portions of any prior art pediclescrews, or may be formed in accordance with the specifications of a newspine stabilizing system. The main requirement of the head portion isthat it serves for either directly being affixed to a rod or other spinestabilizing device or for being affixed to an intermediate device towhich a rod (or other spine stabilizing device and/or other intermediatedevice) can be affixed.

In some embodiments, the pedicle anchor device is a pedicle screw,wherein the shaft is threaded. For example, the thread may have aconstant outer diameter (major diameter), whereas a core diameter (minordiameter) is larger at the proximal side than at the distal side. Thecore diameter may be gradually reduced along the entire length of thethreaded section, or the core diameter has a stepped characteristics, orhas any other characteristics. In other, alternative embodiments, thecore diameter is constant.

In alternative embodiments, the shaft of the pedicle anchor device isnot threaded.

In these embodiments, the shaft may have a non-circular cross section.For example, the shaft may be flattish so as to be blade-like.Especially, the shaft may be such as to have, where it penetrates thepedicle, a larger longitudinal than transversal extension such as tofollow the pedicle's shape. Such a non-circular cross section may inaddition if necessary provide additional stability against twistingmovements.

In special embodiments, the shaft may have a non-circular cross sectionand may be twisted. For example, the shaft may be twisted into about aquarter of a helix so that a blade plane at the distal end isapproximately perpendicular to a blade plane at the proximal end of theshaft. For example, a rod receiving portion (or other means for affixinga spinal column stabilizer) may be oriented relative to the twistedshaft so that the blade plane at the proximal end of the shaft isoriented approximately parallel to a longitudinal direction and at thedistal end of the shaft is oriented approximately parallel to atransversal direction (these terms of direction are to be understood toapply locally, referring to a spine axis). In embodiments of the secondgroup of embodiments where the shaft does not have a circular crosssection but is flattish, the holes from the longitudinal bore outwardmay especially include openings on each of the two flat sides.Additional holes on at least one of the small sides and/or at the distalend may be present. An additional, axial hole at the distal end may beadvantageous during surgery because it allows guidance of the anchorduring insertion by means of a K wire or similar device.

Embodiments of devices and methods in accordance with all aspects of theinvention may be devices/methods for human surgery, or alternatively for(non-human) animal surgery, especially for surgery of dogs, cats orother pets.

In embodiments, the holes through which the liquefied material flows outduring implantation/augmentation, may be on a same axial position, orthey may be at different axial positions. The angular positions may beevenly distributed around the circumference. In special embodiments, theangular positions may have a deviating distribution adapted for aparticular need. For example, if the implant is destined to be animplant for fusing joint parts, and for being inserted in a joint space,the holes (if more than two) may be concentrated on opposed sides to bein contact with the joint areas.

In special embodiments of any aspect of the invention or of any otheranchoring or augmentation process that includes pressing liquefiedmaterial out of holes in a sheath element, a multi-tiered anchoring oraugmentation may be made, with sequentially anchoring/augmenting indifferent tiers, to each tier being attributed at least one outflow hole(and preferably a plurality of outflow holes). To this end, afteranchoring/augmenting on a first tier, an insert element (which may be afirst insert element if the sheath element itself comprises a distalstop face or which may be a second insert element if for theanchoring/augmentation at the first tier already an insert element wasused) is inserted from the proximal side and caused to stop at aposition immediately underneath the second tier. Then, again aliquefaction process is initiated. This may optionally be repeated for athird, or even a fourth, fifth, etc. tier.

In embodiments where the implant does not have a thread, the outer shapeof the implant (and/or of the augmentation device) does not need to begenerally circularly cylindrical but may have any contour.

Mechanical vibration or oscillation suitable for devices and methodsaccording to embodiments of the invention that include liquefaction of apolymer by friction heat created through the mechanical vibration has,preferably, a frequency between 2 and 200 kHz (even more preferablybetween 10 and 100 kHz, or between 20 and 40 kHz) and a vibration energyof 0.2 to 20 W per square millimeter of active surface. The vibratingelement (sonotrode) is e.g. designed such that its contact faceoscillates predominantly in the direction of the element axis(longitudinal vibration) and with an amplitude of between 1 and 100 μm,preferably around 10 to 30 μm. Rotational or radial oscillation ispossible also.

For specific embodiments, a further way for producing the thermal energyfor the desired liquefaction comprises coupling electromagneticradiation into one of the device parts to be implanted and designing oneof the device parts to be capable of absorbing the electromagneticradiation, wherein such absorption preferably takes place within theanchoring material to be liquefied or in the immediate vicinity thereof.Preferably, electromagnetic radiation in the visible or infraredfrequency range is used, wherein the preferred radiation source is acorresponding laser. Electric heating of one of the device parts mayalso be possible.

In this text the expression “thermoplastic material being liquefiablee.g. by mechanical vibration” or in short “liquefiable thermoplasticmaterial” or “liquefiable material” is used for describing a materialcomprising at least one thermoplastic component, which material becomesliquid or flowable when heated, in particular when heated throughfriction i.e. when arranged at one of a pair of surfaces (contact faces)being in contact with each other and vibrationally or rotationally movedrelative to each other, wherein the frequency of the vibration isbetween 2 kHz and 200 kHz, preferably 20 to 40 kHz and the amplitudebetween 1 μm and 100 μm, preferably around 10 to 30 μm. Such vibrationsare e.g. produced by ultrasonic devices as e.g. known for dentalapplications. For being able to constitute a load-bearing connection tothe tissue, the material at the time of insertion has an elasticitycoefficient of more than 0.5 GPa, preferably more than 1 GPa. Theelasticity coefficient of at least 0.5 GPa also ensures that theliquefiable material is capable of transmitting the ultrasonicoscillation with such little damping that inner liquefaction and thusdestabilization of the liquefiable element does not occur, i.e.liquefaction occurs only where the liquefiable material is at theliquefaction interface to the stop face. The plastification temperatureis preferably of up to 200° C., between 200° C. and 300° C. or even morethan 300° C. Depending on the application, the liquefiable thermoplasticmaterial may or may not be resorbable.

Suitable resorbable polymers are e.g. based on lactic acid and/orglycolic acid (PLA, PLLA, PGA, PLGA etc.) or polyhydroxyalkanoates(PHA), polycaprolactones (PCL), polysaccharides, polydioxanones (PD),polyanhydrides, polypeptides or corresponding copolymers or blendedpolymers or composite materials containing the mentioned polymers ascomponents are suitable as resorbable liquefiable materials.Thermoplastics such as, for example, polyolefins, polyacrylates,polymetacrylates, polycarbonates, polyamides, polyesters, polyurethanes,polysulphones, polyaryl ketones, polyimides, polyphenyl sulphides orliquid crystal polymers (LOPS), polyacetals, halogenated polymers, inparticular halogenated polyoelefins, polyphenylene sulphides,polysulphones, polyethers, polypropylene (PP), or correspondingcopolymers or blended polymers or composite materials containing thementioned polymers as components are suitable as non-resorbablepolymers. Examples of suited thermoplastic material include any one ofthe polylactide products LR708 (amorphous Poly-L-DL lactide 70/30), L209or L210S by Böhringer Ingelheim.

Specific embodiments of degradable materials are Polylactides like LR706PLDLLA 70/30, R208 PLDLA 50/50, L210S, and PLLA 100% L, all ofBöhringer. A list of suitable degradable polymer materials can also befound in: Erich Wintermantel und Suk-Woo Haa, “Medizinaltechnik mitbiokompatiblen Materialien und Verfahren”, 3. Auflage, Springer, Berlin2002 (in the following referred to as “Wintermantel”), page 200; forinformation on PGA and PLA see pages 202 ff., on PCL see page 207, onPHB/PHV copolymers page 206; on polydioxanone PDS page 209. Discussionof a further bioresorbable material can for example be found in CABailey et al., J Hand Surg [Br] 2006 April; 31(2):208-12.

Specific embodiments of non-degradable materials are: Polyetherketone(PEEK Optima, Grades 450 and 150, Invibio Ltd), Polyetherimide,Polyamide 12, Polyamide 11, Polyamide 6, Polyamide 66, Polycarbonate,Polymethylmethacrylate, Polyoxymethylene, or polycarbonateurethane (inparticular Bionate® by DSM, especially Bionate 75D and Bionate 65D;according information is available on datasheets publicly accessible forexample via www.matweb.com by Automation Creations, Inc.). An overviewtable of polymers and applications is listed in Wintermantel, page 150;specific examples can be found in Wintermantel page 161 ff. (PE,Hostalen Gur 812, Höchst AG), pages 164 ff. (PET) 169 ff. (PA, namely PA6 and PA 66), 171 ff. (PTFE), 173 ff. (PMMA), 180 (PUR, see table), 186ff. (PEEK), 189 ff. (PSU), 191 ff. (POM—Polyacetal, tradenames Delrin,Tenac, has also been used in endoprostheses by Protec).

The liquefiable material having thermoplastic properties may containforeign phases or compounds serving further functions. In particular,the thermoplastic material may be strengthened by admixed fillers, forexample particulate fillers that may have a therapeutic or other desiredeffect. The thermoplastic material may also contain components whichexpand or dissolve (create pores) in situ (e.g. polyesters,polysaccharides, hydrogels, sodium phosphates) or compounds to bereleased in situ and having a therapeutic effect, e.g. promotion ofhealing and regeneration (e.g. growth factors, antibiotics, inflammationinhibitors or buffers such as sodium phosphate or calcium carbonateagainst adverse effects of acidic decomposition). If the thermoplasticmaterial is resorbable, release of such compounds is delayed.

If the liquefiable material is to be liquefied not with the aid ofvibrational energy but with the aid of electromagnetic radiation, it maylocally contain compounds (particulate or molecular) which are capableof absorbing such radiation of a specific frequency range (in particularof the visible or infrared frequency range), e.g. calcium phosphates,calcium carbonates, sodium phosphates, titanium oxide, mica, saturatedfatty acids, polysaccharides, glucose or mixtures thereof.

Fillers used may include degradable, osseostimulative fillers to be usedin degradable polymers, including: β-Tricalciumphosphate (TCP),Hydroxyapatite (HA, <90% crystallinity; or mixtures of TCP, HA, DHCP,Bioglasses (see Wintermantel). Osseo-integration stimulating fillersthat are only partially or hardly degradable, for non degradablepolymers include: Bioglasses, Hydroxyapatite (>90% cristallinity),HAPEX®, see S M Rea et al., J Mater Sci Mater Med. 2004 September;15(9):997-1005; for hydroxyapatite see also L. Fang et al., Biomaterials2006 July; 27(20):3701-7, M. Huang et al., J Mater Sci Mater Med 2003July; 14(7):655-60, and W. Bonfield and E. Tanner, Materials World 1997January; 5 no. 1:18-20. Embodiments of bioactive fillers and theirdiscussion can for example be found in X. Huang and X. Miao, J BiomaterApp. 2007 April; 21(4):351-74), J A Juhasz et al. Biomaterials, 2004March; 25(6):949-55. Particulate filler types include: coarse type: 5-20μm (contents, preferentially 10-25% by volume), sub-micron (nanofillersas from precipitation, preferentially plate like aspect ratio >10, 10-50nm, contents 0.5 to 5% by volume).

A specific example of a material with which experiments were performedwas PLDLA 70/30 comprising 30% (weight percent) biphase Ca phosphatethat showed a particularly advantageous liquefaction behaviour.

The material of the sheath element (which may be a screw) may be anymaterial that does not melt at the melting temperatures of theliquefiable material. Especially, the sheath element may be of a metal,for example a titanium alloy. A preferred material is titanium grade5.This material, in addition to being generally suited for implantabledevices, has a comparably low heat conduction. Because of this bad heatconduction, the melting zone arising in liquefiable material and at theinterface to the directing structure is heated quickly, without thesurroundings being heated to too high temperatures. Alternativematerials for the sheath element are other metals like other titaniumalloys, stainless steel, ceramics like Zirconium oxides or Aluminumoxides, or hard plastics such as PEEK etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, ways to carry out the invention and embodiments aredescribed referring to drawings. The drawings mostly are schematical. Inthe drawings, same reference numerals refer to same or analogouselements. The drawings show:

FIGS. 1a and 1b an embodiment of an implant or augmentation device;

FIGS. 1c and 1d a distal portion of a variant thereof;

FIG. 2 a cross section through the device of FIGS. 1a and 1b during theimplantation or augmentation process;

FIGS. 3-5 an embodiment of a sheath element of an implant oraugmentation device;

FIG. 6 a detail of a further embodiment of an implant or augmentationdevice;

FIG. 7 a view of an insert element of the implant or augmentation deviceof FIG. 6;

FIGS. 8 and 9 a further embodiment of a sheath element;

FIGS. 10-12 a pedicle screw being an even further embodiment of a sheathelement and being an embodiment of a pedicle anchor device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device schematically depicted in FIGS. 1a and 1b may be a surgicalimplant, for example for being anchored in hard tissue and/or hardtissue replacement material. It may have a function similar to thefunction of a surgical screw, and/or of an anchor (such as a sutureanchor or an implant to which a dental crown is to be mounted), or itmay have a “standalone” function, for example by containing a substanceto be delivered to a surrounding tissue, and/or by containing adifferent device such as an electronic device, etc. Like in all otherembodiments of the invention, the device, if being designed to remain inthe patient's body after surgical operation, may have any function asurgical device anchored in hard tissue and/or hard tissue replacementmaterial may have in surgery. As an alternative to being designed toremain the patient's body after the surgical operation, the devicesaccording to the different embodiments—unless explicitly statedotherwise—may also be a temporary anchor or may be an augmentationdevice, for example as taught hereinafter.

The device 1 is insertable into an opening or a gap or the like of hardtissue and/or hard tissue replacement material, essentially by amovement along an implantation axis 3 that is also considered to be alongitudinal axis of the device. The device comprises a sheath element11 with a proximal wall portion 11.1 that surrounds a longitudinal bore13 open to the proximal side of the sheath element. A distal end portion11.2 terminates the longitudinal bore distally. The distal end portionforms the directing structure. The directing structure comprises a rampportion 12 sloping away in a concave manner from a center around thelongitudinal axis. At the radially outer side of the ramp portion, thewall portion of the sheath element has four holes 14 equally distributedaround the circumference of the sheath element. At angular positionsbetween the holes, the directing structure further comprises walls 15angularly sub-dividing a portion of the longitudinal bore volumecommunicating with the holes 14. In the depicted embodiment, the wallsdon't have constant thickness and taper towards a proximal edge 15.1.

The device further comprises a liquefiable element 21, namely a polymerpin 21 that is adapted to the sheath element to be inserted in thelongitudinal bore 13 from the proximal side.

For the anchoring or augmenting process, the liquefiable element 21 isinserted and brought into a position where it abuts against thedirecting structure. While the sheath element is in contact with hardtissue and/or hard tissue replacement material 31, the liquefiableelement is pressed against the directing structure while energy impingesfrom the proximal side. Under the additional effect of the pressingforce, the liquefied material of the liquefiable element is pressed outthrough the holes 14 and into structures, like pores, surfaceunevenness, inhomogeneities etc. of the hard tissue and/or hard tissuereplacement material 31.

The variant of the sheath element depicted in FIGS. 1c and 1d isdistinct from the above-described embodiment by the following features.

a. Instead of four holes 14 along the circumferential wall, only twosuch holes 14 are present. The directing structure is shapedaccordingly. If the directing structure is symmetric, the symmetry ofthe directing structure is therefore two-fold instead of four-fold as inFIGS. 1 a, 1 b.

b. The ramp portion 12 of the directing structure is not concave butapproximately plane.

c. The holes 14 are not circular or approximately circular but elongate;in the depicted embodiment the axial extension is substantially largerthan the extension along the circumferential direction.

d. The directing structure comprises an additional, distal, axial hole19. A first potential advantage of such a distal hole is guidance.During surgery, a thin element such as a so-called Kirschner wire (Kwire) can be directed to the target location, and a distal end may beprovisionally fixed there. The sheath element may then be positioned bysliding to the target location on the thin element, whereafter the thinelement may be removed. A second potential advantage is an additionaldistal fixation by liquefiable, liquefied material being pressed out ofthe distal hole 19, too, and being pressed into structures of the tissuearound the exit of the distal hole.

All of these features may be present in combination (as depicted inFIGS. 1c and 1d ) or alone (for example, the structure of FIGS. 1 a, 1 bmay be provided with a distal hole 19 with the four holes and thedirecting structure remaining as they are, etc.). They may also beincorporated in any sub-combination (for example, the structure of FIGS.1 a, 1 b may be modified to comprise two holes and a two-fold symmetry,an additional distal hole, but with the concave directing structure andan approximately circular hole shape, etc.

The additional distal hole 19 (if present) may be engineered to servefor pressing out liquefied material or not, depending on therequirements. As a rule, the larger the diameter and the smaller thedepth, the more is there a tendency for the liquefied material to bepressed out. Also the amount of sheath element material around thedistal hole 19 that participates in cooling the material within thedistal hole plays a role. In a sheath element of the kind illustrated inFIG. 1c and made of Titanium, a PLDLA pin has been used as a liquefiableelement. In a distal hole 19 of a diameter of 1.7 mm and a length of 3mm, small amounts of liquefied material have been observed to exitthrough the distal hole in some experiments, whereas in otherexperiments the material froze in the hole. The ratio d/l of 1.7/3 maythus be viewed as a threshold in implants of this kind. For largerdiameters or shorter depths, there is a reliable effect of materialexiting through the distal hole, whereas by smaller diameters orsubstantially larger depths, the outflow may reliably be prevented dueto the material freezing in the hole during the process.

While the particular ratio is characteristic of the shape of FIG. 1 c,the same principle applies to other shapes.

A distal hole of the kind shown in FIG. 1c is not necessarilycylindrical. Rather, other shapes may be used, including irregularelements protruding from the wall inwards into the distal hole.

If the distal hole is dimensioned to cause material to flow out, but thesurgeon does not want material to flow out distally, a simple plug maybe used to close off the distal hole.

More in general, a sheath element of embodiments of the invention maycomprise any one of or any combination of features a.-d. Instead offeature a., any other number of holes may be present. As illustrated inFIG. 2, an advantageous way of causing energy to impinge is by way of asonotrode 35 that is pressed against a proximal end face of theliquefiable element while mechanical vibrations are coupled into thesonotrode. The mechanical vibrations are coupled into the liquefiableelement 21, and the vibration energy is at least partly absorbed at theinterface to the directing structure causing the polymer material of theliquefiable element to at least locally liquefy at this interface. Theangular structuring of the directing structure with the walls betweenthe holes firstly has the function to separate portions of theliquefiable element during liquefaction. Due to this, approximatelyequal amounts of liquefied material is pressed out of every one of thefour holes 14, even if the liquefied material while being pressed out ofthe different holes 14 encounters different resistance. A secondfunction of the walls 15 that protrude distally from the directingstructure body and the stop face is that of energy directors. Theliquefiable material will have a tendency to start liquefying, under theimpact of mechanical vibrations, at edges or other pronounced structureseither of the sheath element or of the liquefiable element itself. Theenergy directing function of the walls 15 is a means for causing theliquefaction to start and take place in vicinity of the holes 14 andnot, for example, at the proximal interface to the sonotrode where tooearly an onset of liquefaction would be undesired.

FIG. 2 illustrates the situation during the anchoring or augmentationprocess if the sheath element is inserted in a pre-made bore in bonetissue 31. Liquefied and re-solidifying material portions 22 pressedinto the surrounding bone tissue 31 and interpenetrating structures ofthe latter strengthen the tissue that may be cancellous bone oraccording replacement material. In addition, if the device is an implantmeant to remain in the patient's body and portions of the liquefiablematerial remain, after re-solidifying, in the sheath element, theconnection provides a solid anchoring.

FIGS. 3-5 show different views of a further embodiment of a sheathelement of a device according to the invention. In addition to thefeatures of the sheath element 11 described referring to FIGS. 1a , 1 b,and 2, the sheath element 11 comprises the following features:

e. A collar portion 11.3 that is for example used to fasten a different,not shown element to the hard tissue and/or hard tissue replacementmaterial.

f. The holes 14 have a longer axial (with respect to the longitudinalaxis) extension and proximally reach further than the edges 15.1 of thewalls 15. The long axial extension is especially suited for devicesdestined to remain in the patient's body, because they cause a largeinterface between liquefied material portions interpenetrating thetissue on the one hand and material portions remaining in the sheathelement on the other hand.

g. The walls 15 have a portion with a constant thickness ending in theedges 15.1.

h. The ramp portion 12 is not spherical but conical, thus its sectionwith a plane going through the longitudinal axis is a straight line andnot concave.

i. The edges 15.1 of the walls 15 slope towards the center.

These features can be realized all in combination (as in the embodimentof FIGS. 3-5) or individually or in any sub-combination, and in anycombination with features a.-d., except that features b. and h. bothrefer to (alternative) ramp portion shapes.

The particular shape of the walls and the ramp portions of theembodiment shown in FIGS. 3-5 features advantages pertaining to themanufacturing of the sheath element. Particularly, it is possible tomanufacture the sheath element by adding the longitudinal bore to apin-shaped blank by drilling and adding, by drilling at an acute angle,the holes 14. In this, the drilling tool may have a conical end portionand may be moved up and down when the holes 14 are made to create theirelongate shape. However, the sheath element 11 of FIGS. 3-5, like sheathelements of the other embodiments of this invention, are not restrictedto sheath elements made by a particular manufacturing method. Rather,other techniques of manufacturing, including machining techniques andcasting techniques, may be used to manufacture the sheath element. Theskilled person will know and/or will find an abundance of literaturepertaining to the manufacturing of, for example, medical devices oftitanium or other metals, ceramics, hard plastics, etc.

FIGS. 6 and 7 show a further embodiment of a medical device. Compared tothe previously described embodiments, the embodiment of FIGS. 6 and 7incorporates the following features:

j. The outer side of the sheath element comprises an outer thread 11.4.

k. The longitudinal bore 13 is a through bore, making the devicesuitable for being guided by a wire in minimally invasive surgery. Thethrough bore is narrowed towards the distal side so that a shoulder 11.5is built. The shoulder serves as a stop structure for an insert element18 that terminates the longitudinal opening for the liquefiable elementtowards the distal side and that comprises the directing structureincluding the walls 15 and the ramp portions 12. The insert elementcomprises a distal tapered portion 19 that together with the shoulder11.5 co-operates to form a force fit.

Features j. and k. may be realized alone or in combination, and there isthe option to combine with any one of features a.-i.

Other stop structures would be possible. For example the sheath elementmay comprise at least one interior axial groove that reaches from theproximal end of the sheath element to a distal stop and in which acorresponding number of ridges or tongues of the insert element isguided. Such an embodiment features the additional advantage that theangular relative orientation of the sheath element and the insertelement is well-defined during insertion. As an even further variant ofa stop structure, the insert element may comprise a spring deflected,during insertion in the sheath element, radially inward against a springforce and forcing a stop flange portion into an annular stop groove ofthe sheath element at the appropriate axial position. Various other stopstructures are possible.

Further features of the embodiment of FIGS. 6 and 7 are:

l. The edges 15.1 of the walls 15 slope towards the center (c.f. featurei.)

m. The walls 15 protrude proximally further than the holes 14. By this,the effect of a controlled distribution of liquefied material betweenthe different holes is effective even if the resistance encountered forliquefied material pressed out of the holes differs strongly between theholes because the interface between liquefied material and still solidmaterial may be expected to be proximal of the upper (most proximal) endof the holes 14 (in contrast to feature f.; feature m. may be combinedwith any other one of features a.-k).

FIG. 8 depicts an embodiment of a sheath element 11 of the kinddescribed referring to FIGS. 6 and 7 that is a surgical screw, forexample a pedicle screw, or an augmentation device that is suitable forpreparing an insertion of a surgical screw, as described hereinafter inmore detail.

FIG. 9 depicts a section along the plane IX-IX in FIG. 8 illustratingoptional features that may be realized in any embodiment, either aloneor in combination.

-   -   The holes 14 are not strictly radial, but axes of the holes, do        not go intersect the proximodistal axis. This brings about an        asymmetry of the holes with respect to clockwise vs.        anticlockwise rotational movements of the device. This in turn        produces sharp edges marked by X in FIG. 9. If the device, after        the anchoring or augmentation process, is turned in a direction        that corresponds to a clockwise rotation in FIG. 9, the        liquefied and re-solidified material remaining in the hole is        subject to both, a shearing force and a cutting action by the        sharp edges X. This will favor a separation between liquefiable        material portions outside of the sheath element and        interpenetrating the hard tissue and/or hard tissue replacement        material on the one hand and liquefiable material portions        remaining in the sheath element on the other hand. A        configuration where an unscrewing corresponds to a clockwise        rotation in FIG. 9 is thus advantageous in cases where the        device is an augmentation device, where the sheath element is to        be retracted. If, on the other hand, the device after anchoring        is turned in a counter-clockwise direction, the force acting on        the liquefied and re-solidified material in the holes 14 will        have a radial and an axial component, with reduced shearing        forces, and no cutting occurs. In such a situation, there will        be a strong resistance to a rotational movement. A configuration        where an unscrewing corresponds to a counterclockwise rotation        in FIG. 9 is thus advantageous in cases where the device is        designed to remain anchored in the body of the patient.    -   The holes 14 are not at equal axial positions. Rather, the        positions may follow the thread. This feature may be        advantageous if the sheath element comprises a thread, although        an interruption of the thread—if the holes are at equal axial        positions or have another axial position distribution—is in most        cases not a problem.

The principle of the outflow holes being asymmetrical with respect to aradial direction may be implemented independent of the described aspectof the invention. It may be used for medical devices comprising a sheathelement suitable of being brought into contact, during a surgicaloperation, with live hard tissue and/or with hard tissue replacementmaterial, which is based on the liquefiable material being inserted(pre-assembled or inserted in situ) in a longitudinal bore of the sheathelement and where the sheath element comprises at least one hole in thesheath element wall, through which the liquefied material is pressedfrom the longitudinal bore into the structures (pores or cavities orother structures) of the bone tissue or other hard tissue or hard tissuereplacement material in which anchoring is desired.

The hereinbefore described embodiments may, in addition or as analternative to the mentioned optional features, be provided in thefollowing variants:

-   -   Multi-tiered anchoring or augmentation with a plurality of        insert elements sequentially inserted, the second, more proximal        insert element inserted after anchoring or augmentation with the        first, more distal insert element, or with a distal directing        structure of the sheath element and with at least one insert        element to be placed proximally of the distal directing        structure after anchoring with the latter. In this, the sheath        element comprises one or more holes for each of the different        insert elements or for the distal directing structure and the at        least one insert element. The sheath element may comprise a        plurality if inner shoulders that have a stepwise reduced cross        section towards the distal side, or may comprise different        guiding grooves reaching to different distal positions for the        different insert elements.    -   The number of holes 14 attributed to a particular directing        structure does not need to be four as in the illustrated        embodiments but may be two (like in FIGS. 1c and 1d ), three,        five, six, etc. Also, the angular (azimuthal) spacing does not        need to be equal between all holes but may be adapted to a        particular situation. For example, for introduction of an        implant in a gap of a joint, the sheath element may comprise two        pairs of neighboring, relatively close holes at opposite sides.        In the case of multi-tiered anchoring, each tear may have an        individual number and distribution of holes.    -   The holes may have different shapes and/or different sizes.

The multi-tiered anchoring or augmentation as described herein thuscomprises a first liquefaction process taking place with a firstdirecting structure, —of the sheath element or of an initially separateinsert element—the subsequent (after an at least partialre-solidification of the liquefied material) addition of a furtherdirecting structure of a (second) insert element and then a secondliquefaction. This multi-tiered anchoring or augmentation may be appliedindependent of the aspect of the invention, i.e. also in situationswhere a directing structure against which the liquefiable material ispressed is not angularly structured.

Referring to FIGS. 10, 11, and 12, a bone screw, namely a pedicle screw41 based on the first aspect of the invention is depicted.

The pedicle screw 41 comprises a screw head 42, a threaded section 43,and a distal end portion 44. The pedicle screw further comprises alongitudinal through bore 13 that, towards the distal end, comprises anarrowed portion so that a shoulder 11.5 for stopping the insert element(not shown in FIGS. 10-12, the type thereof may for example be similarto the one of the device of FIG. 7) inserted from the proximal side isformed.

The thread has a constant outer diameter (major diameter), whereas acore diameter (minor diameter) is larger at the proximal side than atthe distal side. More concretely, in the depicted embodiment, in acentral portion of the threaded section the core diameter graduallyreduces, whereas in peripheral portions the core diameter is constant.In other, alternative embodiments, the core diameter is constant, isgradually reduced along the entire length of the threaded section, orthe core diameter has stepped characteristics as taught in WO 90/02526,or has any other characteristics. Also, the outer diameter of thethreaded section need not be constant. Generally, the approach accordingto aspects of the invention may be combined with any suitable outerthread. Compared to prior art pedicle screws with a longitudinal bore,the bore diameter is comparably large to make insertion of theliquefiable element—that may be a polymer pin—possible. In the depictedembodiment, the bore diameter at the more proximal portion of thethreaded section is 3.1 mm and at the distal portion of the threadedsection is 2.9 mm, whereas the major diameter is 6.6 mm and the minordiameter is between 4.4 mm and 5.3 mm. The resulting wall strength hasproven to be sufficient.

The screw head is flattened and comprises an inner thread that can beused for coupling to an apparatus for automated insertion, as describedhereinafter.

What is claimed is:
 1. A medical device, comprising: a sheath elementsuitable of being brought into contact, during a surgical operation,with live hard tissue and/or with hard tissue replacement material, thesheath element having a longitudinal bore defining a longitudinalopening reaching from a proximal end of the sheath element into a distaldirection, and a plurality of holes in a wall of the opening, aliquefiable element that is insertable or inserted in the longitudinalopening and at least partly liquefiable by the impact of energyimpinging from the proximal side so that liquefied material flowsthrough the holes in the wall and out of the longitudinal opening intostructures of the hard tissue and/or hard tissue replacement material, afirst distal stop face against which a distal end of the liquefiableelement is pressable for liquefaction, the first distal stop face beingat a first position, and an insert element comprising a second distalstop face, the insert element insertable from a proximal side into thelongitudinal opening and shaped to be stopped at a position in which thesecond distal stop face is at a second position different from the firstposition.
 2. The device according to claim 1, wherein the first distalstop face is a distal stop face of the sheath element.
 3. The deviceaccording to claim 1, wherein the insert element is a second insertelement, and wherein the device further comprises a first insert elementthat comprises the first distal stop face.
 4. The device according toclaim 3, wherein the longitudinal bore is a through bore and comprises astop structure, the first insert element being shaped to rest againstthe stop structure when inserted from the proximal side.
 5. The deviceaccording to claim 1, wherein at least one of the distal stop facesforms a directing structure having a structure that varies as a functionof the azimuthal angle with respect to a longitudinal axis of thelongitudinal opening to direct different portions of the liquefiablematerial to different ones of the holes.
 6. The device according toclaim 1, wherein the sheath element further comprises an outer thread.7. The device according to claim 1, wherein the first position isimmediately distally of at least a first one of the holes and whereinthe second position is immediately distally of at least a second one ofthe holes.
 8. The device according to claim 1, wherein the sheathelement has an outer contour that is different from a circular cylinder.9. The device according to claim 1, wherein the sheath element has aplurality of inner shoulders to have a stepwise reduced cross sectiontowards the distal side.
 10. The device according to claim 1, whereinthe sheath element has a plurality of guiding grooves reaching todifferent distal positions.
 11. The device according to claim 1,comprising a further insert element shaped to be inserted into thelongitudinal opening from a proximal side and to stop at a thirdposition proximally of the second position.
 12. The device according toclaim 1 being an implant.
 13. The device according to claim 1 being anaugmentation device equipped for reinforcing hard tissue and/or hardtissue replacement material by the liquefiable material interpenetratingstructures of the hard tissue and/or hard tissue replacement material.14. The device according to claim 1 being a pedicle anchor device forbeing implanted in a human or animal vertebra from a generally dorsaldirection through one of the pedicles of the vertebra so that a distalportion of the anchor device protrudes into the vertebral body of thevertebra, the pedicle anchor device comprising a proximal head portionfor securing an orthopaedic device for stabilizing the spinal column,and comprising a distal shaft portion capable of being anchored in thevertebra, the longitudinal opening reaching from the proximal headportion into the shaft portion.